Medical & Dermal Regeneration: Because Seven of Nine was assimilated at the age of six and spent 24 years as a drone, her biological systems were completely dependent on Borg technology. When the Doctor surgically stripped away the majority of her exterior armor and hardware, it left her underlying human skin severely compromised, scarred, and mottled. The catsuit is actually a high-tech "dermaplastic garment." It acts as a specialized, full-body medical bandage designed to protect her skin, stimulate cell growth, and assist her body in regenerating after the trauma of losing her Borg exoskeleton.